The present invention relates in general to the use of low level electric fields to control movement of fish.
In the operation of a hydro-electric plant, in which a dam is constructed across a river or stream to facilitate generation of electricity with water driven turbines, a problem is often presented with respect to the fish and other aquatic life in the river or stream. In particular, fish are frequently killed or injured by being swept over a dam's spillway, or into the turbines. In addition, the turbines can be damaged if fish are ingested into them, especially in the case of smaller turbines and large fish, such as eels. Numerous attempts have therefore been made to prevent fish from approaching these off-limits areas.
In an effort to solve the foregoing problem without the need for costly, difficult to maintain physical barriers, the inventor experimented with the use of electric field barriers in a river, other bodies of water and other hydraulic works associated with hydroelectric power projects which prevent the fish from approaching off-limits areas by subjecting them to stun-inducing electric shocks. While certainly effective at stopping the fish from swimming, this technique proved to be less than desirable for two reasons. First, because the stunned fish can not swim until they recover, only the water currents in the river or stream will determine the path of their movement once they are stunned. If the area being protected is a turbine intake at a hydro-electric plant, this likely means that the stunned fish will be swept directly into the intake, thereby completely defeating the purpose of the electric field barrier. Second, the likelihood that the fish will be permanently injured by being stunned in this manner is substantial. In particular, examinations of fish exposed to stun-inducing fields which appeared to have recovered from being stunned, confirmed that many of the fish were found to have sustained permanent skeletal damage.